There's a scientist in the UK who apparently spends most of her time studying large breasts:

Dr Joanna Scurr, lecturer in bio-mechanics at the University of Portsmouth, said: “Breasts are getting bigger but it’s not just because we’re getting heavier.

We looked at 300 British women over four years and found an increase in the size of the average bosom, not just in women who are fat.”

So over time women's breasts are getting larger, but no one is quite sure why it's happening. If only we could duplicate (or quadruplicate) the phenomenon at will.

[Mystery behind mega boobs revealed! - Times of India]